The present invention relates to high speed generators and, more particularly, to a hydraulic mount for high speed generators used with gas turbine engines such as those used in aircraft, tanks, ships, vehicle, terrestrial, or other applications.
Generator systems for aircraft may include three separate brushless generators, namely, a permanent magnet generator (PMG), an exciter, and a main generator. The PMG includes permanent magnets on its rotor. When the PMG rotates, AC currents are induced in stator windings of the PMG. These AC currents are fed to a regulator or a control device, which in turn outputs a DC current. This DC current next is provided to stator windings of the exciter. As the rotor of the exciter rotates, three phases of AC current are typically induced in the rotor windings. Rectifier circuits that rotate with the rotor of the exciter rectify this three-phase AC current, and the resulting DC currents are provided to the rotor windings of the main generator. Finally, as the rotor of the main generator rotates, three phases of AC current are typically induced in its stator windings, and this three-phase AC output can then be provided to a load such as, for example, an aircraft electrical system.
Because some aircraft generators are variable frequency systems that rotate in the speed range of 12,000 rpm to 24,000 rpm, potentially large centrifugal forces may be imposed upon the rotors in generators. Given these potentially stressful operating conditions, the rotors should be precisely balanced so the generator is balanced.
Even though high speed aircraft generator rotors generally are precisely designed, producing a rotor with some imbalance is generally difficult due, for example, to variations in manufacturing processes. A rotor imbalance may cause the rotor to vibrate, and deviate from its intended axis of rotation. The amplitudes of such vibration can be fairly significant if the rotor""s rotational speed reaches its resonance speed, or a multiple of its resonance speed. Such speeds are generally known as xe2x80x9ccritical speeds.xe2x80x9d If an imbalanced rotor is rotating at one of the critical speeds, it may be damaged.
In view of the foregoing, one approach is to prevent operation of the generator at such critical speeds. In particular, a generator may be designed so that the critical speeds are either well above the normal operating speed range, well below the normal operating speed range, or a combination of both. In the latter two cases, where one or more of the critical speeds is below the rotor""s normal operating speed range, the rotor is operated through the critical speeds on its way up to the normal operating speed range. Thus, to avoid damage, the rotor may be quickly brought through a critical speed to achieve a higher normal operating speed.
In addition to quickly bringing the rotor through critical speeds, it is also known to dampen rotor vibrations as the rotor passes through critical speeds. One known method for dampening rotor vibrations is to provide oil in the form of squeeze film between a stationary housing and the bearing liner in the rotor assembly. Such a design is undesirable under circumstances where the mount on which the rotor rotates stiffens quickly with increased loading as the rotor imbalance increases. This circumstance can cause one or more of the critical speeds to increase toward the operating speed range. In this manner, this design does not control the critical speed or speeds as may be desired.
Therefore, there is a need for a high speed generator with a rotor mounting system that successfully dampens the rotor vibration at the critical speeds, and/or that does not rapidly stiffen with increased loading, and/or that allows one or more critical speeds to be controlled. The present invention addresses one or more of these needs.
The present invention provides a system for hydraulically mounting a high speed generator rotor that dampens the rotor""s vibration at its critical speeds, and/or that does not rapidly stiffen with increased loading, and/or that allows the critical speeds to be controlled.
In one embodiment of the present invention, and by way of example only, the system for hydraulically mounting a high speed generator shaft includes a bearing assembly, a cylindrical bearing liner and at least a first inlet oil port. The bearing assembly includes a bearing inner race concentrically mounted on the shaft. The bearing assembly is surrounded by the bearing liner. The bearing liner has an inner circumferential surface and an outer circumferential surface and is dimensioned such to form a gap between the bearing outer race and the bearing liner inner circumferential surface. The first inlet oil port is formed in the bearing liner and extends between the bearing liner inner circumferential surface and the bearing liner outer circumferential surface.
Other features and advantages of the preferred hydraulic mount will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention.